Liquid flow control arrangement

ABSTRACT

A monitor arrangement for controlling liquid flow rate in a line which passes before drop sensing means which sense the passage of drops. Drop trigger means are coupled to and responsive to the drop sensing means and provide an output pulse at the passage of each drop. Triggered by this output pulse are time trigger means which provide a pulse of a predetermined time interval. Logic and comparison means are coupled to said drop and time trigger means to judge the flow rate and motor means are in turn driven by said logic and comparison means. A line valve is responsive to the motor means which regulates the liquid flow in the valve.

United States Patent Stobble et al.

[54] LIQUID FLOW CONTROL ARRANGEMENT [72] lnventors: Richard P; Stubble,l-laines City;

' Richard V. Knapp, Winter Haven,

both of Fla.

[73] Assignee: Nilsen Mfg. Co., l-laines City, Fla.

[22] Filed: March 2, 1971 [21] Appl. No.2 120,209

[52] US. Cl ..250/218, 250/222 PC, 250/209,

128/214 E, 24/275 [51] Int. Cl. ..G0ln 21/26 [58] Field of Search..250/218, 222 PC, 231, 209; 356/208, 28; 128/214 E, 214 F, DIG. l3;

[451 Oct. 24, 1972 Primary Examiner-Walter Stolwein Attorney-George B.Oujevolk [57] ABSTRACT A monitor arrangement for controlling liquid flowrate in a line which passes before drop sensing means which sense thepassage of drops. Drop trigger means are coupled to and responsive tothe drop sensing means and provide an output pulse at the passage ofeach drop. Triggered by this output pulse are time trigger means whichprovide a pulse of a predetermined time interval. Logic and comparisonmeans are 222/52 422 coupled to said drop and time trigger means tojudge the flow rate and motor means are in turn driven by [56]References Cited said logic and comparison means. A line valve is UNITEDSTATES PATENTS responsive to the motor means which regulates the liquidflow in the valve. 3,450,153 6/1969 Hildebrandt et al.128/214 XE 9Claims, 9 Drawing Figures r I I l IO w Isa f] 4 I I I 1 w' 1 I4 I 4 I Il 2 24 L p I J 2 26 DROP (lzoms) RATE /(360/|O26MS) SLAVE\/ (9OMS) 11 To 5 T R ii T 3 I CLOSE OPEN 32 OK PMENTEDUBI 2 I972 3.700.904

SHEET 3 [IF 6 +5v 240 r 7 A 22b B a2 a m Q R 0 O O 0 O O Q O O O C O O O0 DROP o/s RATE o/s SLAVE ms 0 o 0 o 0 0 D T 0 T fi SW FLOW RATE CONTROLBUFFER AMP.

INVENTOR. FIG. 3 & ard P. Qtobbe Richard 1. Knapp George B O AeHLflkPATENTEU um 24 m2 SHEET 8 0F 6 ALARM ENABLE fFLOW RATE R'mhard P Stobbe"IN VENTOR.

LIQUID FLOW CONTROL ARRANGEMENT BACKGROUND OF THE INVENTION BRIEFDESCRIPTION OF THE PRIOR ART At present, several venoclysis regulatorsare commercially available. In its simplest form, the regulator may bemerely an adjustable clamp placed on the liquid delivery tube. Such anarrangement is crude and its usefulness varies with the skill of thetechnician doing the laboratory work. Other devices are more usefulhaving a drop counter and displaying the flow rate in digital form,e.g., ml per hour. In still other arrangements, an alarm is provided ifthe feed rate exceeds or is below a predetermined quantity per hour. Inall of these systems presently available, certain defects exist whichpreventthe instrument from providing correct information under manycircumstances and which furthermore provide false information dangerousto hospital patients under. certain circumstances.

Except for the very crude arrangement using only a clamp, mostcommercially available liquid flow monitoring instruments will have theflowing liquid pass before sensing means in drop quantities, and, atfirst glance it seems. a simple task to design a device which will countthe number of drops in a given time period. One of the firstdifficulties encountered is whether or not the sensing means see a dropor is the sensing means receiving an extraneous light signal which isprovidinga false reading. Since all drops are not clear liquid, e.g.,sometimes the instrument is used with blood, the sensing means mustfunction over a broad range of drop characteristics as to size andopacity. Also, the instrument must be operable in many places other thanin shielded sick rooms. Places where, for instance, the sensing meanswill be exposed to extraneous light as from flashlights of technicians,sixty cycle flicker of fluorescent lighting, paper charts in the nurseshands, etc. The sensing means must therefore have the ability todistinguish between the disturbance of the light as seen by thephotoelectric cell as produced by a falling drop of fluid from thatproduced by any other means.

Furthermore, the flow of a liquid in a narrow tube depends on thehydrostatic reaction between the tube and the liquid, e.g., thecapillary propensities of the tube, the adhesion and viscosity of theliquid, the temperature of the liquid, etc., and, one of the most commonproblems encountered will be that of liquid adhesion to the sensingmeans and condensation on the inside surfaces of the drip chamber infront of the sensing means caused by splash from the falling drops.Since the instrument is designed for use with a great variety ofliquids, the problem cannot readily be solved merely by a chemicalsurface coating on the sensing means which repels the liquid, e.g., asilicone substance in the case of a water-type liquid. It must beanticipated that in many cases, liquid often clings to and sometimesfogs the inside of the drip chamber wall thus restricting the visibilityof the sensing means. This condition could increase in magnitude to apoint where a sensing means would fail to detect the drop. This wouldresult in erroneous data and faulty control.

Still another problem is to control the liquid flow au- I tomatically.Assuming that the sensing'means properly senses the drops, theinstrument then needs a servo loop to properly control the liquid flowrate to agree with a predetermined setting. Also, in the event ofstoppage of flow, as when the bottle is empty, to provide an alarm.

SUMMARY OF THE INVENTION Generally speaking, the present inventioncontemplates a monitor arrangement for controlling liquid flow rate inthe form of drops falling in line which passes before drop sensing meanswhich sense the passage of drops. Droptrigger means are coupled to andresponsive to thedrop sensing means and provide an output pulse at thepassage of each drop. Triggered by this output pulse are time triggermeans which provide a pulse of a predetermined time interval. Logic andcomparison means are coupled to said drop and time trigger means tojudge the flow rate and motor means are in turn driven by said logic andcomparison means. A line valve is responsive to the motor means whichregulates the liquid flow in the valve.

The invention as well asother objects and advantages thereof will bemore apparent from the following detailed description when consideredtogether with the accompanying drawings in which:

FIG. 1 is a block schematic diagram of the logic circuitry contemplatesherein;

FIG. 1a represents the applicable binary outpu waveforms from the DROPand SLAVE one-shots also the resulting NAND gate output and the truthtable for the condition OK;

FIG. 1b represents the applicable binary output waveforms from the DROPand RATE one-shots, also the resulting NANDgate output and the truthtable for the condition Close;

FIG. 10 represents the applicable binary output waveforms from theDROP,the inverted RATE, and the inverted SLAVE one shots, also the resultingtruth table for the condition Open; FIG. 1d shows a truth table;

FIG. 2 is a block diagram of the entire instrument contemplated herein;

FIGS. 3a and 3b show a schematic explanation and diagram of theinstrument contemplated herein;

FIG. 4 is an explanation of the clamp setting arrangement; and,

FIG. 5 shows a front view of the instrument contemplated herein.

DETAILED DESCRIPTION Logic FIGS. I, la, lb, 1c, 1d

' To first understand the operation of the instrument, it isadvantageous to appreciate the logical determinations which are firstmade by the instrument. Having an understanding of the instrument logic,it is then possible to follow the block diagram explanation of theinstrument, which will provide the function of the several componentscooperating in carrying out the desired functions. After this, it isthen possible to explain the circuitry of each of the individualcomponents which will cause these components to perform their functions.

Shown in FIG. 1, is a block diagram of the logic circuitry used in theinstrument contemplated herein and FIGS. 1a, 1b,1c,1d,are logic diagramwaveforms and truth tables produced by the diagram of FIG. 1. Thecomponents represented by the block diagram of FIG. 1 are: a liquidcontainer with a drip chamber 12 passing between a lamp l4 and a pair ofphotocells 16a and 16b. The outputs of the photocells 16a and 16b arefed to a differential amplifier l8, and to the buffer amplifier 20 whichis the interface element between the differential amplifier l8 and thedrop one-shot 22. .The trigger means consisting of three monostablemultivibrators-22, 24, 26, also known as one-shots, and marked with thelegends DROP, RATE and SLAVE. Associated with the three multivibratorsor one-shots are three NAND gates 28, 30, 32. Those skilled in the artwill readily understand that the use of a NAND gate or AND gate is.merely a matter of circuitry designs and one can be substituted for theother by redesigning the logic. The situation depicted in the wave formfigures, FIGS. la to lo relates to the second and subsequent drops andits time relationship to the previous drop of liquid. Only threepossible situations exist: l) the subsequent drop is on time or OK; (2)the subsequent drop arrives too soon in which case it is necessary toclose the clamp thereby decreasing the liquid flow; (3) the subsequentdrop arrives too late in which case it is necessary to open the clampthereby increasingthe liquid flow. The situations will be determined bythe logic block acting upon various states of the one-shots during thedrip pulse time interval. At the conclusion of the drip pulse, i.e., thetrailing edge of the waveform, the system is reset. The reset isaccomplished by re-triggering the RATE one-shot 24so that the pre-settime period is started again.

Going back now to FIG. 1, it is noted that the container 10 is above thetwo photocells and that the drop forming chamber passes verticallybefore the two photocells 16a and 16b. Thus, the drop will pass firstbefore photocell 16a and at a later time period before photocell 16b.Any ambient light will strike both photocells 16a and 16bsimultaneously. Therefore, since the output of the differentialamplifier 18 is the difference in signal outputs from photo-cells 16aand 16b, it follows that when the first drop passes 16a there will be apositive signal which will peak, i.e., reach a maximum at a time whenthe drop fully covers photocell 16a, and will decrease as the dropcontinues to fall to zero when the drop is equally covering photocells16a and 16b. The output of differential amplifier 18 will changepolarity and reach a peak at the opposite polarity at the time the dropcovers photocell 16b. Thus, any light which originates outside the dropforming chamber will have little effect on the output since this willeffect both cells equally. In addition, should a droplet or fog coveronly one cell there will be no output from the differential amplifier 18since the photocell outputs are capactively coupled to the differentialamplifier and couple only rapid changes such as would be produced by thepassing of a drop.

The signals from the photocells 16a and 16b, approximately like a cosinewaveform in character, are combined in the differential amplifier l8 andfurther processed in the buffer amplifier 20 so as to insure posi- 'tivetriggering of the DROP monostable multivibrator (herein called aone-shot). The first one-shot 22 triggers off another square wave intothe second one-shot 24 which serves as the time reference and the secondone-shot 24 then triggers off another square wave'into the thirdone-shot 26 herein termed the SLAVE oneshot. As is well known andconventional, the input line to the one-shots is identified as T(trigger), and the outputs are identified as D and D from the DROPoneshot, R and R from the RATE one-shot, and S and S from the SLAVEone-shot. Associated with the three one-shots are three NAND gates 28,30, 32 with inputs 34, 36, for gate 28; 38, 40 for gate 30; 44, 46 forgate 32; and outputs 48, S0, 52 respectively for gates 28, 30, i 32. I

The first one-shot 22 may be considered as the DROP one-shot; the secondone-shot 24 is the RATE one-shot; the third one-shot 26 is termed theSLAVE one-shot which is triggered by the RATE one-shot. Although thesetime periods are not critical, in a practical instrument, the DROPone-shot is of 120 millisecond duration, and the SLAVE one-shot is ofmillisecond duration. The RATE one-shot is set by the flow rate controland thus will provide pulses of varying width depending on thesetting.In a typical unit, this may vary between 360 and 2000 milliseconds. TheDROP one-shot 22 is connected from the D output to inputs 34, 42, and 44of the NAND gates, and thus supplies a pulse to all three NAND gates.The RATE oneshot 24 is connected from the R output to gate 30, input 40,so that one output is fed to the first NAND gate and the-inverted outputto the second NAND gate. The slave output to the third NAND gate 32through input 46 and from S output tothe second NAND gate 30 throughinput 39. v

To repeat the foregoing, the first one-shot D output goes to the first,second, and third NAND gates; the second one-shot R output goes to thefirst NAND gate and the Routput goes to the second NAND gate; the thirdone-s hot S output goes to the third NAND gate, while the S goes to thesecond NAND gate. The first and third NAND gates have two inputs, thesecond NAND gate has three inputs. Since the first one-shot representsthe DROP and the second one-shot the desired pre-set time between drops,an output from the first NAND gate means that the drops are passing toofast and the valve should be closed, i.e., the subsequent drop appearedduring the second one-shot time period. The third one-shot supplies asignal to the third NAND gate afier the pre-set time lapse. Therefore,if an input appears simultaneously from the first one-shot whichrepresents the DROP and the third one-shot representing the previousdrop, at the third NAND gate, then, the drops are passing on time andthe flow rate is OK which is the output provided by the third NAND gate.

The second one-shot represents the rate, and all-three one-shots areconnected to the second NAND gate so that if the drops are flowing tooslowly the valve should be opened.

The foregoing situation is given in truth tables which are shown in thedrawing for convenience of understanding. Furthermore, to enhance theaccuracy of the device, it is also possible to use a drop periodaveraging arrangement, e.g., a register operating over a span of atleast two drop periods.

With the. foregoing understanding of the logic used herein, it ispossible to understand the block diagram of the arrangement hereincontemplated and depicted in FIG. 2. Here, the container is repeatedwith the drip chamber 12 shown passing before the sensing meansconsisting of lamp 14 and photocells 16a and 16b. As previouslyexplained,the photocell output is fed to the differential amplifier 18,interface buffer amplifier 20, three one-shots 22, 24, 26, which in turnare coupled to the logic 27 consisting of NAND gates 28, 30, 32 (theexpression NAND gate also broadly including an AND gate). Mentionheretofore has been made of a valve 'which is shown in block diagram asa tube clamp 52.

The tube clamp 52 has a manual control 54 and is also motor controlledby motor 56 which in turn is driven by motor drive bridge 58. The motor56 is geared down to about 1 rpm and will run only a maximum of the DROPone-shot period for each drop. Motor drive bridge 58 is in turncontrolled by logic 27, namely by the three NAND gates 28, 30, 32 whicheither will inhibit motor drive, drive the motor to close the clamp ordrive the motor to open the clamp. The instrument also has an alarm 60which 'is enabled by the logic, an alarm solenoid component 62 to shutthe flow of liquid and an amplifier 64 to the solenoid. The power supplyis shown as block 66.

ClRCUITRY FIGS. 3a, 3b

In the middle of the schematic wiring diagram 3a is shown lamp 14 whichconsists of a standard incandescent bulb 13. Opposite the light bulb 13at the bottom of FIG. 3a of the schematic drawing, are the twophotocells 16a, 16b. Each cell has a cell bias resistor 17a, 17b. Thus,with light from bulb 13 illuminating the cells, the cells are balancedand no output signal is emitted. The cell circuitry also includes ACcoupling capacitors 19a, 19b, which prevent the differential amplifier18 from going into saturation in the event the level of illumination tothe photocells is unbalanced as when condensation occurs on the dripchamber interior surface. The photoelectric cells 16a and 16b also haveappropriate biasing resistors 17a and 17b, the capacitors 19a, 19bproviding the coupling into the differential amplifier 18 which also hasappropriate bias resistors 18a and 18b. Load resistors are also shown.The photocells and the differential amplifiers are commerciallyavailable units and the differential amplifier is sold as an integratedcircuit. The output of the differential amplifier 18 goes to the bufferamplifier 20.

The buffer amplifier includes a transistor and other appropriatecircuitry which together with the succeeding stage DROP one-shot 22includes timing RC resistor 22a, capacitor 22b. This unit and thesucceeding oneshots are commercially available integrated circuitcatalog items. The three one-shots 22, 24, 26 have already beendescribed in connection with the explanation of the logic in FIGS. 1,la, 1b and 1c. The second one-shot 24 is connected to switch flow ratecontrol 29 having resistors 29a, 29b, 290, etc., and a switch 29s. Byturning the switch 29s to the appropriate resistor, the RC of the secondone-shot 24 may be varied to desirable time settings. A furthercalibration adjustment of the RATE one-shot is provided by a transistor24r connected to switch 29s and RATE one-shot 24.

Logic 27 has also been previously explained and since gating circuitryexplanation is well understood by those skilled in the art, and theunits used for the three NAND gates are commercially available, circuitdetails are omitted. As shown, there are three output lines from thelogic 27. Lines 27a and 27b go to the motor drive bridge 58. Line 27c isthe OK line and by-passes bridge58. Line 27c also is an alarm reset lineand will be discussed in connection with alarm conditions. Lines 27a and27b each lead to a driver transistor in bridge 58, line 27a going todriver transistor 57 while line 27b goes to driver transistor 59. Drivertransistors 57 and 59 operate transistors 57a, 57b, and 59a, 59b. Thesetransistors in turn form the motor drive bridge and cause the motor 56to turn in the one or the other direction. The motor 56 is geared downto drive the clamp screw at about 1 rpm.

The alarm 60 includes variable resistor 61a, which is ganged to theswitch flow rate control 29 and capacitor 63. These components will acton the alarm solenoid 62 which will release a spring acting on clamp 52shown in FIG. 2, so as to shut the liquid flow. The other components inthe alarm system are the amplifier transistors 64a and 64b, thecompound-alpha circuit transistors 67 (also known as DarlingtonCoupling) into the alarm resistor diodes 64c, and 64d. The alarm disableflip-flop circuit 77 and its associated alarm reset line 270 connectingthe alarm disable circuit and the logic 27.

As previously explained, the time lapse of the second one-shot 24depends on the setting of the flow rate control switch 29. Ganged withthis switch is alarm resistor 61a, which together with alarm capacitor63 set the alarm time. The alarm also includes an input transistor a anddiode 75b. The alarm delay time period is set by the alarm RC circuitand is somewhat longer than the time lapse setting between drops for thesame setting by the flow rate RC circuit.

The DROP one-shot output D is coupled to transistor 75a and diode 75b tocapacitor 63. Capacitor 63 is discharged through 61a. The charge oncapacitor 63 is sensed by the compound-alpha transistor 67. When thischarge drops to a low level, the transistors are returned to anon-conducting state, causing the voltage at the driver transistor 57 toincrease, and is coupled through diode 64c to the base of transistor64b. This causes transistor 64b to conduct through transistor 64a, whichis allowed to conduct any time the DROP one-shot is not in a timingcycle, thus completing the circuit through the alarm relay coil 71. Aswitch is then operated completing a trigger circuit allowing current toflow to an alarm solenoid 62 and tripping the spring loaded clamp 52.When the clamp is released, it overrides the control setting on the tubeclamp established .in normal operation and clamps the tube off and stopsthe flow completely. This trip action also operates a switch whichremoves the +12 volt power from the control circuitry and applies it tothe alarm lamp 95.

A second switch is also operated at the same time and its terminals aremade available for external alarm circuits.

Since transistor 64b is enabled also in the normal the same time as theCLOSE or OPEN transistor in on, thus if the liquid flow is interruptedlong enough for the capacitor 63 to discharge, the alarm circuit wouldbe activated.

' Under conditions in actual use, the alarm conditions could besatisfied erroneously during the set-up or start of the regulator beforethe servo balance has been established. This could become a nuisancefactor. In order to overcome this factor, an alarm latch circuit 77 isused in which the components are selected such that when the power isturned on, the bistable multivibrator transistor 83a is conducting whichclamps transistor 83b off. The alarm enabled lamp 81 is turned off andline 77a is at voltage which is coupled to the compound-alpha circuit 67clamping the output transistor in a conducting state which prevents thealarm circuit from operating so long as the bistable alarm latch is inthis state. When the period between drops coincides with the presetrate, this latch receives a pulse from the logic gate on line 27c andcauses the alarm latch transistor 83b to conduct, turns on the enabledlamp 81, clamps transistor 83a base, and the line 77a to thecompound-alpha circuit to ground. This serves two purposes, namely, thealarm bistable latch is clamped in the enable state, and the ground lineis coupled through a suitable resistor to the emitter-base junction ofthe compound-alpha transistors 67,

enabling it to sense the capacitor 63 voltage and stabilizes thetransistor pair. If the normally open switch 79 is pushed, the alarmlatch is again placed in the alarm disabled state, but automaticallyresets itself the first time a drop falls-in the correct time period.This feature eliminates thepossibility of human error in forgetting toreset the alarm. It also serves as a visual indication that theregulator is in control.

MECHANICAL FEATURES Line clamp 52, as shown in FIG. 4, consists of onefixed jaw 87 and one movable jaw 85. Jaw 85 is responsive to theposition of threaded member 91, surface 91a relative to fork surfaces85c as pivoted on pin 85b threaded member 91 is engaged with screw 89which in turn is fixed to the shaft of motor 56, through thrust bearing96 so that this screw 89 is only free to rotate with the shaft of motor56. The threaded member 91, on the other hand may be manually rotatedwhich allows it to move in and out thereby controlling the clampadjustment. The motor 56 is always free to respond to the logic commandsof the system. Friction between the fork 85c and surface 91a on thethreaded member 91 may only move in and out on the thread of the screw89 as this screw is driven by the motor thereby controlling the clampadjustment.

Throughout the normal clamping range, the fork 85d is free to move alongthe surface 90a of the shaft 90. Shaft 90 is held, as shown in FIG. 4 bysear lever 98 and with spring 94 compressed. When the condition foralarm exists, solenoid 62 is energized causing plunger 62b to operatesear lever 98 thus releasing shaft 90 so that the spring 94 will drivethe, shaft 90, and with it fork 85d causing the clamp jaw 85 to closeori the fluid line stopping the flow. The button surface 93 on shaft 90is now extended through the control panel and acts I as a visualindication as to the status of the alarm mechanism. Reset can beaccomplished by depressing 8 the surface 93 until spring 94 is againcompressed and the sear lever 98 again locks the shaft 90 in the reset"position.

In summary, the clamp may be controlled by the motor 56, the manual knob54 which is connected to the threaded member 91, or by the spring loadedshaft 90 which only has two states, either shut down where it overridesthe clamp adjustment established .by fork 850, or in the reset positionwhere it cannot interfere with the clamp jaw at all.

The instrument is shown in FIG. and the face plate shows the flow ratecontrol switch 29s as a dial, the clamp jaws 85 and 87 with its manualcontrol 54, the reset button 93, the alarm enable lamp 81, as well as analarm lamp 95 which is lit by the alarm condition.

It is to be observed therefore, that in the present" instrument anelectro-mechanical arrangement replaces the usual screw type clamp andcontinuously makes adjustments to correct for the numerous factors thatattempt to change the flow rate. A time comparison is made between thedrop period and an internal reference. Digital logic circuits make thedecision as to the action that must be taken to correct the flow rateand then sends a signal to the motorized clamp which completes theaction. This is a type of servo loop which can only stabilize when thetime period between drops is exactly what is called for by the operatorwhen the rate control is set on the front panel. The time to check andcorrect is approximately 0.2 seconds so even at the fastest rate, eachand every drop is checked and the clamp adjusted whenever called for. Aphotoelectric drip-sensor head is attached to the drop forming chamber.Photoelectric cells are illuminated by a small lamp so that the drop canbe detected as it falls to the fluid pool at the bottom of the chamber.The resulting electrical signal is the input to the logic section of theregulator. The instrument utilizes transistors, diodes, and integratedcircuits, all solid state for cool operation, economy, and long life,and requires only standard l05-l30 volt AC line and consumesapproximately 12 watts.

In the present instrument, use is made of a No. 330 lamp operating at areduced voltage to peak photocell output and increase life. Thephotocells are matched, positioned vertically so that the drip shadowfalls on each cell at different times, and responds to ambient lightequally. A differential amplifier is used to amplify this drop signal toa useful level. A buffer amplifier provides the interface between thedifierential amplifier and the DROP one-shot. A monostable multivibratorone-shot is used to further process the drop signal by cutting off theripple associated with the drop signal, so that only one output pulseexists for each drop. The time period for this one-shot is selected sothat the first ripple blanks out all the succeeding ripples for thedrop, then resets and awaits the next drop. Thus, the period should beslightly longer than the time it takes for the drop to fall past thephotocells. The DROPoneshot output pulse triggers the timing one-shotwhich is adjustable by means of the flow rate control switch. When thisperiod is over, it triggers the SLAVE oneshot. The SLAVE one-shotfunctions as the OK period generator, its time is fixed and if the dropfalls while the. slave is in its period, the motor will not run.

For the purpose of giving those skilled in the art a better appreciationof the invention, the following illustrative example is given:

VENOCLYSIS OPERATING PROCEDURE The venoclysis set is assembled withbottle and needle, suspended from the stand and the tube purged untilfree of air.

The regulator control unit is clamped to the stand post, positioned sothat the top clears the drip chamber. The drop sensor unit is attachedto the drip chamber. The tubing is guided into the regulator clamp jawsand under the protective ledges above and below the clamp. The tube isstretched slightly to work down in the clamp jaws. It may be necessaryto depress the reset button and turn the manual control c.c.w. to openthe clamp jaws fully. The manual control is turned clockwise to squeezethe tube shut. All other clamps are opened. The drip chamber wall isdepressed to bring the fluid level up to the line indicated on the dropsensor. The Rate control is set to the desired time to dispense 1 literof fluid. The venipuncture made, the manual control is adjusted until aslow drip is established. The power cord is plugged in, the power switchis snapped on, the alarm disable button depressed. (When the alarmenabled light (green) comes on, the approximate rate is established.)The alarm remote cable between the alarm jack on the control unit to thenurse call receptacle is connected.

In the event the flow is interrupted or the bottle is empty, the alarmis activated and the tube is clamped shut with some fluid left in thedrip chamber so that the tube does not require purging when changingbottles. The red lamp comes on and the nurse call circuit is activated.After the cause for the interruption is corrected or the bottle ischanged, the regulated flow will start after the manual reset button isdepressed.

If the patient must be moved, the power cord and the nurse call remotecable must be unplugged. The bottle and regulator can now go with thepatient. The flow will continue at the established rate, but will notregulate until the power cord is plugged in again.

The alarm disable switch and the alarm enabled (green) light are bothexternal components of the alarm system. Because of the nature of thesystem there are conditions when the alarm could trip needlessly so adisable switch is provided. Also, since it could be left in the disabledstate by accident, a circuit that automatically enables the alarmcircuit is provided. The green light shows when this alarm is ready. Themechanism that enables the alarm system to set itself is the drip thatcomes approximately in the correct time period. Because of this, itfollows that the control system is operative. This does not mean thatthe drip rate is exactly correct. It may in fact take several minutes tostabilize and become accurate.

We claim:

1. In an instrument for controlling liquid flow rate in a line, saidinstrument having light sensitive drop sensing means for sensing thepassage of drops, drop trigger means coupled to and responsive to saiddrop sensing means providing a pulse at the passage of each drop or afixed plurality of drops, time trigger means coupled to and triggered bysaid drop trigger means providing a pulse of a predetermined time width,logic and comparison means coupled to said drop and time trigger meansto judge the flow rate, motor means coupled to and driven by said logicand comparison means, line valve means connected to and driven by saidmotor means to regulate the liquid flow in said line, the improvementtherein, wherein said drop trigger means and said time trigger means andsaid logic and comparison means includes first, second and thirdmonostable multivibrators, said first multivibrator responding to apulse input supplied by said drop trigger means, a variable resistorcapacitor time switch including means for time setting, said switchbeing coupled to said second multivibrator, said second multivibratorconnecting said first and third multivibrators, first, second, and thirdAND/NAND gates and logic circuitry connecting said gates and saidmultivibrators providing separate outputs if a succeeding drop is:timely with respect to a preceeding drop, too soon thereafter, or toolate thereafter, and a bridge coupled to said gates responsive to saidoutput, said motor means being connected and driven by said bridge.

2. An instrument as claimed in claim 1, said drop sensing means beingfirst and second light sensing cells sensing at least one drop passagebefore said cells so disposed that each drop must first pass before thefirst and then the second photocell.

3. An instrument as claimed in claim 2, including a differentialamplifier coupled to said cells, one cell being coupled to the invertedinput of said differential amplifier providing an output only onreceiving drop inputs from said cells at different times.

4. An instrument as claimed in claim 1, including first and seconddriver units connected to said bridge to drive said motor means in theone or the other direction.

5. An instrument as claimed in claim 4, including an alarm variableresistor capacitor time circuit, spring means, spring latch means andsolenoid means, said spring means biasing said valve means to shut theline, said latch means inhibiting said latching, said solenoid removingsaid latch means, and, an alarm logic circuit connected between saidlogic and comparison means, said alarm time circuit, and said solenoidto shut said line in case of alarm.

6. An instrument as claimed in claim 5, said alarm time circuit beingganged to said time switch, said alarm time resistor capacitor circuitproviding a comparatively longer time for alarm than the correspondingsetting on said time switch, and an alarm power circuit connectedbetween said motor means and said alarm circuit, and said motor means orsaid solenoid means.

7. An instrument as claimed in claim 6, including an alarm disablecircuit connected to said alarm power circuit to temporarily disablesaid alarm having a reset line connected to the logic and comparisonmeans.

8. An instrument as claimed in claim 7, said valve means including firstand second clamp faces, one of said clamp faces being mounted on one offirst and second threaded members, one of said members being connectedto said motor means and a hand set means for turning the other member.

9. An instrument as claimed in claim 1, including a drop periodaveraging means coupled to said drop sensing including storage meansoperating over a span of at least two drop periods in order to enhancethe accuracy of the drop sensing means.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 700,904Dated October 24, 1972 Invent r( P.

It is certified .that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

On the cover sheet [72] the name 0f the first inventor should readRichard P.' Stobbe Signed and sealed this 15th day of May 1973.

(SEAL) A'ttest:

EDWARD M.FLETCHE R,JR. I I ROBERT GOTTSCHALK Attesting Officer CCommissioner of Patents FORM PO-105O (10-69) l JSCOMM-DC 60 376-P69 atus. GOVERNMENT PRINTING OFFICE: 1969 0-366-334.

1. In an instrument for controlling liquid flow rate in a line, saidinstrument having light sensitive drop sensing means for sensing thepassage of dropS, drop trigger means coupled to and responsive to saiddrop sensing means providing a pulse at the passage of each drop or afixed plurality of drops, time trigger means coupled to and triggered bysaid drop trigger means providing a pulse of a predetermined time width,logic and comparison means coupled to said drop and time trigger meansto judge the flow rate, motor means coupled to and driven by said logicand comparison means, line valve means connected to and driven by saidmotor means to regulate the liquid flow in said line, the improvementtherein, wherein said drop trigger means and said time trigger means andsaid logic and comparison means includes first, second and thirdmonostable multivibrators, said first multivibrator responding to apulse input supplied by said drop trigger means, a variable resistorcapacitor time switch including means for time setting, said switchbeing coupled to said second multivibrator, said second multivibratorconnecting said first and third multivibrators, first, second, and thirdAND/NAND gates and logic circuitry connecting said gates and saidmultivibrators providing separate outputs if a succeeding drop is:timely with respect to a preceeding drop, too soon thereafter, or toolate thereafter, and a bridge coupled to said gates responsive to saidoutput, said motor means being connected and driven by said bridge. 2.An instrument as claimed in claim 1, said drop sensing means being firstand second light sensing cells sensing at least one drop passage beforesaid cells so disposed that each drop must first pass before the firstand then the second photocell.
 3. An instrument as claimed in claim 2,including a differential amplifier coupled to said cells, one cell beingcoupled to the inverted input of said differential amplifier providingan output only on receiving drop inputs from said cells at differenttimes.
 4. An instrument as claimed in claim 1, including first andsecond driver units connected to said bridge to drive said motor meansin the one or the other direction.
 5. An instrument as claimed in claim4, including an alarm variable resistor capacitor time circuit, springmeans, spring latch means and solenoid means, said spring means biasingsaid valve means to shut the line, said latch means inhibiting saidlatching, said solenoid removing said latch means, and, an alarm logiccircuit connected between said logic and comparison means, said alarmtime circuit, and said solenoid to shut said line in case of alarm. 6.An instrument as claimed in claim 5, said alarm time circuit beingganged to said time switch, said alarm time resistor capacitor circuitproviding a comparatively longer time for alarm than the correspondingsetting on said time switch, and an alarm power circuit connectedbetween said motor means and said alarm circuit, and said motor means orsaid solenoid means.
 7. An instrument as claimed in claim 6, includingan alarm disable circuit connected to said alarm power circuit totemporarily disable said alarm having a reset line connected to thelogic and comparison means.
 8. An instrument as claimed in claim 7, saidvalve means including first and second clamp faces, one of said clampfaces being mounted on one of first and second threaded members, one ofsaid members being connected to said motor means and a hand set meansfor turning the other member.
 9. An instrument as claimed in claim 1,including a drop period averaging means coupled to said drop sensingincluding storage means operating over a span of at least two dropperiods in order to enhance the accuracy of the drop sensing means.